Fix bug#70856

* lisp/pixel-scroll.el (pixel-scroll-precision-scroll-down)
(pixel-scroll-precision-scroll-up): Apply finer threshold for
the minimum unit of scrolling.
(pixel-scroll-precision-scroll-down-page): Document true
restrictions on DELTA.  (bug#70856)

(cherry picked from commit 671c9e08b2286d8c32ac6ca00eadc4c8d5e1d5e4)

diff --git a/lisp/pixel-scroll.el b/lisp/pixel-scroll.el
index 4bf912e54c0ac65afb63680056ae5129924ff757..20c7f3fe59608e1949a5262a3330cb6e90dcd7bd 100644 (file)
--- a/lisp/pixel-scroll.el
+++ b/lisp/pixel-scroll.el
@@ -501,8 +501,8 @@ Otherwise, redisplay will reset the window's vscroll."
 ;;;###autoload
 (defun pixel-scroll-precision-scroll-down-page (delta)
   "Scroll the current window down by DELTA pixels.
-Note that this function doesn't work if DELTA is larger than
-the height of the current window."
+Note that this function doesn't work if DELTA is larger than or
+equal to the height of the current window."
   (let* ((desired-pos (posn-at-x-y 0 (+ delta
                                        (window-tab-line-height)
                                        (window-header-line-height))))
@@ -551,8 +551,7 @@ the height of the current window."
 
 (defun pixel-scroll-precision-scroll-down (delta)
   "Scroll the current window down by DELTA pixels."
-  (let ((max-height (- (window-text-height nil t)
-                       (frame-char-height))))
+  (let ((max-height (1- (window-text-height nil t))))
     (while (> delta max-height)
       (pixel-scroll-precision-scroll-down-page max-height)
       (setq delta (- delta max-height)))
@@ -666,8 +665,7 @@ to `pixel-scroll-precision-interpolation-factor'."
 
 (defun pixel-scroll-precision-scroll-up (delta)
   "Scroll the current window up by DELTA pixels."
-  (let ((max-height (- (window-text-height nil t)
-                       (frame-char-height))))
+  (let ((max-height (window-text-height nil t)))
     (when (> max-height 0)
       (while (> delta max-height)
         (pixel-scroll-precision-scroll-up-page max-height)